This invention relates to sputtering processes and more particularly to an anode plate configuration in an RF sputter deposition system for achieving more uniform dielectric film deposition on substrates.
In the formation of thin passivating layers on substrates by RF cathode sputtering, such as forming quartz layers onto semiconductor wafers placed on an anode, problems of layer uniformity occur depending upon the location of the wafers on the anode. It is found that the thickness of the layers tends to drop off at the edges of the wafers. This problem is more severe with the wafers which are located around the outer portions of the anode, especially along the outer edges of the wafers which have no wafers adjacent to them. This non-uniformity causes difficulties in integrated circuit manufacture because the layer thickness of the edges may be insufficient to provide the needed passivation on chip sites located close to the edge of the wafer. The non-uniformity across the wafer also can result in processing difficulties where the chips at the edge would reach etch completion before those at the center.
Ways of achieving better coating uniformity have been proposed, for example, the article "Compensation Mechanism for Uniform Sputtering" by H. M. Gartner et al., IBM Technical Disclosure Bulletin, Vol. 19, No. 2, pps 516-517, July 1976, in which the distances between the wafers and the cathode are varied depending upon the wafer location by the use of spacers, pedestals or grooves of different thickness. The closer the wafer to the cathode, then the thicker the coating.
We have now found that, in order to maintain the uniformity of coating quality, the surfaces of the wafers should be located in the same plane. Also, the thickness of the anode plate under each wafer should be uniform to maintain each wafer at the same potential to improve uniformity. Furthermore, it has been found that the edge drop off problem is primarily related to the resputtering condition at the anode rather than the amount of incident material from the cathode. A lower anode potential along edges of the outermost wafers is believed to cause less resputtered material to be deposited in those areas than elsewhere, then causing the observed thickness drop off.